<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>内置对象</title>
</head>
<body>
        <script>
            var r = Math.random();
            var c = Math.ceil(12.3);
            console.log(r);         //打印出来的是0.6961218977516139
            console.log(c);         //打印出来的是13
        </script>
</body>
</html>